Accessing UI Widget data from .ccp file in .c file

[020394]

Hello all,
I am trying to get data input from a line widget and use it in a .c file , is there a way to do it ? I am able to pass int data from .c file to cpp file and show it in the UI using extern"C"{c codes};
I tried using it with the C++ codes , but to no avail , there are plenty of errors.
Please Teach me a way to pass data from .cpp file to .c file Thank you

[anda_skoa]

You retrieve the QString from the QLineEdit in C++, convert it to an 8-bit encoding, e.g. using QString::toUtf8(), and then pass the char* or const char* data from the resulting QByteArray to the C function.

The char* data is valid as long as the QByteArray object is.

Cheers,
_

[020394]

Hello thanks for the immediate reply , i did this , when i click a button it will do this
QString a=QString::toUtf8(ui->lineEdit->text());
I am unsure of how to pass the char* to c function . Please help

[anda_skoa]

First, toUtf8() is not a static method, it is an instance method and has to be called on a QString instance.
Second, assigning its result value to a QString object again would get you nothing other than a needless (and possibly wrong) double conversion.

As I said, toUtf8() (and other methods to convert to 8-bit encodings such as toLocal8Bit()) return a QByteArray

QByteArray data = ui->lineEdit->text().toUtf8();
printf( "%s", data.constData() );

QByteArray data = ui->lineEdit->text().toUtf8();
printf( "%s", data.constData() );

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using printf() as an example for a C API.


Cheers,
_

[020394]

First, toUtf8() is not a static method, it is an instance method and has to be called on a QString instance.
Second, assigning its result value to a QString object again would get you nothing other than a needless (and possibly wrong) double conversion.

As I said, toUtf8() (and other methods to convert to 8-bit encodings such as toLocal8Bit()) return a QByteArray

QByteArray data = ui->lineEdit->text().toUtf8();
printf( "%s", data.constData() );

QByteArray data = ui->lineEdit->text().toUtf8();
printf( "%s", data.constData() );

To copy to clipboard, switch view to plain text mode 

using printf() as an example for a C API.


Cheers,
_

Thanks Again , I now understand how to convert the QString to a array.
Now the Probelm is passing it to the C file.
this is what i did
Codes:
#include <stdio.h>
#include "mainwindow.h"
extern "C++" {QByteArray data;}
char hi()

{
printf( "%s", data.constData() );
}
i gotten many errors about namespace.
Please advice me on how to do the codes in C.
The thing i dont know is how to pass C++ object(eg. QByteArray) to C codes.
Thank you in advance !
Really sorry i am not good in Qt or c codes. I am a newbie.

[Santosh Reddy]

Linking C and C++ code

[anda_skoa]

Thanks Again , I now understand how to convert the QString to a array.

Then why don't you use that?

void hi( const char *data )
{
    printf( "%s", data );
}
 
QString s = "....";
QByteArray d = s.toUtf8();
hi( d.constData() );

void hi( const char *data )
{
    printf( "%s", data );
}

QString s = "....";
QByteArray d = s.toUtf8();
hi( d.constData() );

To copy to clipboard, switch view to plain text mode 

Cheers,
_

[020394]

Then why don't you use that?

I am using that in my .cpp file.
I am getting the String from a LineEdit in my cpp file called mainwindow
I followed ur code by setting this

QByteArray data=ui->lineEdit->text().toUtf8();

QByteArray data=ui->lineEdit->text().toUtf8();

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Now I want to pass the QByteArray data to the c file .
I am passing it to the c file to query it from the database using sqllite statment.

I tried calling the object from the cpp file to c file
Using

extern "C" QByteArray data;

extern "C" QByteArray data;

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But i dont think i am able to retrieve the data from the cpp file

I am getting errors such as unknown type "namespace".
.

[020394]

void hi( const char *data )
{
    printf( "%s", data );
}
 
QString s = "....";
QByteArray d = s.toUtf8();
hi( d.constData() );

void hi( const char *data )
{
    printf( "%s", data );
}

QString s = "....";
QByteArray d = s.toUtf8();
hi( d.constData() );

To copy to clipboard, switch view to plain text mode 

Cheers,
_[/QUOTE]

Btw this code is the .cpp or the .c file ?
I do not need to declare a QString now . as i am just using the ui->lineEdit->text(); to get the data

[anda_skoa]

Btw this code is the .cpp or the .c file ?

In cpp of course, it contains C++ code (usage of classes).

Now I want to pass the QByteArray data to the c file .

No, you want to pass the const char* to the C file. The QByteArray type is a C++ class not a C type

Cheers,
_

[020394]

Thanks anda_soka for your help, I now understand how to pass the QByteArray to my .c file already . The main problem is I was not sure of how to use the extern properly. Thanks to Santosh Reddy for giving me the link to the extern information . Really appreciate your help